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<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
   
     class EventEmitter {
       constructor(){
          this.subs = Object.create(null)
       }
       //注册事件
       $on(eventType,handler){
        this.subs[eventType] =  this.subs[eventType] || []
        this.subs[eventType].push(handler)
        console.log(this.subs[eventType])
       }
       //触发事件
       $emit(eventType){
         if(this.subs[eventType]){
          this.subs[eventType].forEach(handler => {
            handler()
          });
         }
       }   
     }
     let em = new EventEmitter()
     em.$on('click',()=>{
       console.log("click1")
     })
     em.$on('click',()=>{
       console.log("click2")
     })
     em.$emit('click')






  </script>
</body>
</html>